The present invention relates to a structure and driving method of a plasma display panel, and more particularly to the structure and driving method of a plasma display panel having three electrodes.
Generally speaking, a plasma display panel (PDP) is a matrix-type display device and adopts a line-sequence driving method which lengthens the light-emission time, to double the number of signal lines of a dot-sequence driving method. An extended light-emission time enhances luminance. However, for DC color PDPs, the device itself is inefficient when compared with that used for a monochrome PDP. Therefore, luminance suffers when adopting the line-sequence driving method to a DC color plasma display panel, which is typically used only for monochrome plasma display panels.
To overcome the luminance deficiency, PDP driving methods have been proposed which protract the light-emission time for one field. One example of such a method is a so-called memory type driving method, wherein, if a cell is turned on once, it stays on for one field or one sub-field. In other words, while a plasma display panel using the line-sequence scanning method performs writing and erasing operations during every horizontal scanning period, in the memory type PDP, cells turned on for one horizontal scanning period stay illuminated for the duration of the next horizontal scanning period. Here, if the memory-type plasma display panel is operated using space charge, the panel is classified as a DC panel, and if the panel uses wall charge, it is classified as an AC panel.
FIG. 1 is a conventional plasma display panel showing the structure of a DC pulse, memory-type plasma display panel disclosed by NHK of Japan.
Referring to FIG. 1, the plasma display panel has a front plate 1 and a backing plate 2. Two writing anodes 3 and one auxiliary anode 4 are alternately and horizontally (or vertically) arranged in striped form on front plate 1. Backing plate 2 has a plurality of cathodes 5 vertically (or horizontally) arranged in striped form and a plurality of barriers 6 which surround both a writing discharge area 7 for discharge with writing anode 3 and an auxiliary discharge area 8 for discharge with auxiliary anode 4.
FIG. 2 shows waveforms applied to the respective electrodes of the plasma display panel in FIG. 1.
Referring to FIG. 2, when cathodes K.sub.1, K.sub.2, K.sub.3 are sequentially scanned, an auxiliary discharge cell is discharged to continuously supply charge particles to a main discharge area. Here, if a main discharge should be created, a writing pulse is loaded before a sustaining pulse so that a cell of cathode K.sub.1 generate discharge. Then, the sustaining pulse is continuously applied to maintain the discharge. The sustaining and scanning pulses should not coincide with each other, so that cells in which a writing-discharge is created stay on, while those in which a writing-discharge is not created stay off. That is, the auxiliary anode supplies charge particles, while the main anode is used for the writing and sustaining of discharge and the cathode is used for erasing the discharge.
However, the structure and driving method of the above plasma display panel has the following disadvantages:
First, writing discharge cells and auxiliary discharge cells (not used for writing) are disposed on the same plane. This is unfavorable for high resolution displays.
Secondly, since sustaining as well as writing discharges are performed by the main anode, its line resistance comes into question. In memory type panels, if the line resistance is great, all the cathodes under the main anode may be turned on, resulting in high current flow through the main anode and thus a large voltage drop. This would reduce operating margin. In practice, indium-tin-oxide (ITO) and Ni each have line resistances high enough to cause the above problem. The use of Au or Ag reduces line resistance, but since mercury adhering to the cathodes' surface is used in such cases to suppress damage thereto due to ion bombardment in DC memory-type PDPs, electrical opens may develop.
Thirdly, when a plurality of cells under one anode are turned on, the output impedance of a driving circuit should be low, such that the necessary driving waveforms are complicated.